Electrode arrangement



M r 1956 P. LEMAlGRE-VOREAUX 2,738,435

ELECTRODE ARRANGEMENT Filed Dec. 14, 1950 .nvenm- United States PatentELEC'IRDE ARRANGEMENT Pierre Lemaigre-Voreaux, Paris, France, assignerto Societe Anonyme pour les Applications de lElectricite et des GazRares-tablissements Claude-Fez & Silva, Paris, France, a company ofFrance Application December 14, 1950, Serial No. 200,7 68

Claims priority, application France December 20, 1949 3 Claims. (Cl.313-40) This invention relates to an electrode arrangement forelectrical discharge apparatus.

One object of this invention is to provide an electrode arrangement forelectrical discharge apparatus wherein a metal wire, wound and coatedwith emissive materials, is attached to an electrically conductingsupport, which may be a current connection for the electrode, at leastat one point, said one point being located at one end of the wire or inthe immediate vicinity of said end.

Another object is to provide a support for the coated wire of anemissive electrode, which support is in contact, locally at least, witha fin of heat conducting materiai, which may form a portion of thesupport.

One feature of the invention consists in providing the support of theelectrode wire with a fin, the distance between the support and the finbeing not more than 1 millimeter along the support from the penetrationplace of the support into the inner atmosphere of the dischargeapparatus up to at least one contact point of said fin with said supportand to the attachment point of said electrode wire to said support.

One advantage of the invention is to avoid that the electrode be put outof use prematurely in some cases, said putting out of use being causedby the fact that either the small wire portions which connect the woundportion with the supports, or the supports themselves, happen to break.This may happen, particularly, when the electrode is mounted in adischarge apparatus subjected, at the time of its starting, to arelatively high voltage, higher than 500 volts, for instance. Theputting out of use is said to be premature, when it occurs before analmost total exhaustion of the emissive materials on the electrode.These breakings should probably be attributed to an excessive heating ofthe parts in question, due to a higher density of the cathode glow onsaid parts than on the rest of the electrode, or even to cathode spotsforming on said parts during the starting period which lasts for thetime of the voltage application to the time when a discharge with a lowcathode drop is normall initiated on the winding coated with emissivematerials.

Other objects, features and advantages of the invention will in part beobvious, and will in part be explained hereinafter.

In drawings which illustrate embodiments of the in vention,

Figure 1 is a side elevation of a wound-wire-support assembly,

Figure 2 is an end view of the assembly shown in Figure 1.

Figure 3 is a side elevation of another woundwire support assembly.

Figure 4 is an end view of the assembly shown in Fig. 3.

Figure 5 is a side elevation of yet another wound-wire support assemblyand,

Figure 6 is an end view of the assembly shown in Figure 5.

In the assembly shown in Figures 1 and 2 the wire,

wound and coated with emissive oxides, is secured by pinching, to theends 2 and 3 of two supports, constituted by current leads 4 and 5. Fins6, 7 are secured to the current leads 4 and 5 respectively by weldedspots 8 and 9 located between the stem 10 in which the current leads aresecured, and the point of attachment of the winding 1.

The electrode proper consists, as known, of,a double wound refractorymetal wire, coated with emissive mate rials composed of alkaline earthoxides partly reduced at the time of the formation of said electrode.The ends 12, 11, of winding 1 are secured, respectively, to the lead-inwires 4, 5 by pinching said ends in the hooks 2, 3 terminating saidlead-in wires. These pinchings are efiected as close as possible to theends of the winding, so as to decrease as much as possible the lengthsof the wire por tions placed between each lead-in wire and the woundportion, saidportions being most fiable to break under the action ofstartings; the precaution is taken, after the winding has been securedto the supports 4 and 5, of mov ing the ends 2 and 3 of the currentleads slightly closer together so as to move the end turns of winding 1doser together, since these turns loosen slightly during the winding ofthe wire. The winding is coated with the emissive alkaline earthcompounds after it has been secured on the current connections.

The fins 6, 7 may be made, for instance, of nickel sheet 0.2 mm. thick.In the case shown, each of them has the shape of an approximatelyisoceles triangle, the case of which, 14, 18 or 13, l7, is very closethe lead 4 or 5; the fins are located at little distance from the planecontaining the current leads 4 and 5. The apices 13 and 14 of thesetriangles protrude, in the direction of the discharge (i. e. towarclsthe upper portion of the figure), and extend in this direction, beyondthe winding. The apices 13 and 14 point approximately in the directionset the discharge at the ends of the winding; in the presentcase, sincenothing is acting as a screen in the vicinity of the electrode, thesedirections are close to each other and are in the general direction ofthe arrow 20. The points of the fins at 13 and 14 facilitate theinitiation of the discharge when the apparatus having the electrode hasa voltage applied thereto.

The fins thusarranged form good heat conducting surfaces, which are incontact with or in the vicinity of the supports and the non-woundportions of the electrode; they decrease the temperature rise of theseparts. These parts, where they do not touch the adjacent fin, arecooled, since the gas layer separating them from the adjacent fin isvery thin. In Figures 2, 4 and 6, the spacing between the current leadshown and its fin has been exaggerated so as to make it visible, but, inpractice, it can be decreased to a fraction of a millimeter without anydif ficulty. Experience has shown that for distances greater than 1 mm.between the fin and current lead, the effect of the fin isinSufiicie-nt; the result obtained becornes botter as these distancesbecome smaller. For reasons of convenience in manufacture, the lowerportions 2), 21, of the current leads are not completely covered by thefins. T his olers no drawback since these portions of the current leads,having no point less than 1 mm. from the closest point of thecorresponding fin, are cooled by the latter; further, they are alsocooled by thermal conductivity through the portions 22, 23 inside thestem.

Figures 3 and 4 show a modification in which the ends of the winding arepinched in lugs such as 24, cut out in the fins. To pass from onesupport-lead to winding 1, the current must fiow though thecorresponding fin itself which may thus be considered as part of thesupport and as supporting the winding. The lugs may also be out fromnickel strip and welded to the fin.

Figures 5 and 6 show another type of embodiment in which the winding isattached by welding to the current leads and at points intermediatebetwen those where the leads corne out of the stem and those where thefins are attached. Each fin is very close to the current lead, from thestem, or nearly from the stem, to the point 25 where the fin is weldedto the lead closest to the stem; thus protection is provided for allpoints of the current lead on which the discharge would have a tendencyto concentrate during the starting period.

The following numerical example gives dimensions which gave good resultsin one particular case; an order of magnitude of the dimensions to beadopted in other cases can easily be derived therefrom.

The electrode, of the type shown in Figures 1 and 2, is designed for afluorescent lamp 2.5 mm. long and 25 mm. in diameter, of an usual typeexcept as regards the electrodes. This lamp, which comprises two similarelectrodes, is supplied with an alternating current of 0.3 ampere; itsoperating voltage is approximately 300 volts. When the lamp is inposition in its sockets, the two current leads to each electrode areconnected together outside the lamp so as to be at the same potential;the starting without any preheating is ensured by the open circuitvoltage of the power supply apparatus, said voltage reaching about 650volts.

Winding l, neglecting its activating coating, is formed as a helix 3 mm.long and 1 mm. outside diameter; it is obtained by winding on a mandrela molybdenum wire, 0.1 mm. in diameter, on which a molybdenum wire 0.05mm. in diameter has been previously wound, and thereafter removing themandrel. The current leads, inside the lamp, are nickel wires, 0.6 mm.in diameter, about 8 mm. long, from the point where they corne out ofthe stem to the point where the ends of the Winding are se curedthereto. Each fin forms a triangle With an approximate area of 31 mrnfl,and it has been eut out of a nickel strip 0.2 mm. thick. The lampprovided with electrodes thus protected can start more than 100,000times before it is put out of use, which then coeurs by an exhaustion ofthe emissive material coating the Winding 1.

Numerous modifications may be made in the above described electrodes.The Windings coated with thermoemssive materials may be of a variety oftypes and may be attached to one support only or to three or more; oneor more of these supports may not be used as a current lead. In casethere is more than one support, it is often unnecessary that allsupports be provided with fins. For instance, in the case of usualfluorescent larnps, with bipolar electrodes and starting by pre-heating,it is generally unnecessary for the supports which connect the activatedWinding with the preheating interrupter to carry fins; it is preferable,however, that all the supports carry fins so that special bases andsockets are not required for preventing connection of the lamp in amanner which connects the current source to the supports not providedwith fins. The latter may have varied shapes and orientations, they mayreceive a coating facilitating their thermal radiation, for instance bysuperficially carburizing the metal they are made of; several fins mayof course be used on the same support.

What I claim is:

1. An electrode mount for an electric discharge lamp having an innerspace, comprising a stem, a metal wire and an assembly formed ofelectrically conducting supports extending from said stem into saidspace and a fin in contact with each of said supports at least at onepoint and each spaced from its respective support at other points, saidfins being made of heat conducting material, said metal wire beingwound, coated with emissive matcrials and electrically connected to saidsupports, the distance between each support and its correspondin g finbeing not more than one millimeter along that portion of the supportextending from said stem to the point of contact of the support with thefin, said fins lying in a plane close and parallel to said metal wire.

2. An electrode mount as set forth in claim 1, wherein the ends of thewire are attached directly to the fins.

3. An electrode mount as set forth in claim 1, wherein each fin issubstantially triangular in shape and is secured to its correspondingsupports at its base.

References Cited in the file of this patent UNITED STATES PATENTS1,388,793 Birdsall Aug. 23, 1921 2,366,292 Smith Jan. 2, 1945 2,462,837Braunsdorfi Mar. 1, 1949

